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ANTIMONY                                        251

and the sulphides washed thoroughly with hot water containing a little
sodium sulphide and dissolved in nitric acid (D 1-2).

1.  Determination of the Lead.—The nitric acid solution is evaporated
in presence of excess of sulphuric acid until white fumes appear, taken up
in a little water and mixed with a few c.c. of -95% alcohol:; after some
time, the lead sulphate separated is collected in a Gooch crucible as indi-
•cated for the determination of lead in ordinary brasses (see p. 226).

2.  Determination   of  the   Bismuth.—The  liquid  freed  from  lead
sulphate is heated to expel the alcohol and treated with hydrogen sulphide
to precipitate the bismuth and the copper.   The precipitate is filtered 'off,
"washed with hydrogen sulphide solution acidified with a few drops of sul-
phuric acid, and dissolved in a little nitric acid (D 1-2).    The solution is
evaporated in presence of sulphuric acid, taken up in a little water, neu-
tralised  almost  completely with sodium  hydroxide,  and heated gently
with a slight excess of sodium carbonate and a little potassium cyanide.
The bismuth precipitate thus obtained is collected on a filter, washed,
dissolved in nitric acid and again precipitated with ammonia under the
conditions indicated for the determination of bismuth in lead.

3.  Determination of the Copper.—The filtrate from the bismuth—
after treatment with sodium carbonate and potassium cyanide (see 2)—
is acidified with nitric acid and a few drops of sulphuric acid, evaporated
to dryness, taken up in hot water and the copper in the solution determined
by the usual methods.

4.  Determination of the Iron.—The filtrate obtained after removal
of the bismuth and copper as sulphides (see 2) contains all the iron, which
is determined by expelling the excess of hydrogen sulphide, oxidising with
nitric acid and precipitating with ammonium chloride and ammonia.

5.  Determination of the Arsenic.—See Determination of Arsenic in

6.  Determination   of   the   Sulphur    (Hollard   and   Bertiaux).—5
grams of the sample are treated with nitric acid to which sufficient hydro-
chloric acid is added to give a clear solution.   The liquid is evaporated to
dryness, taken up again in nitric acid and evaporated several times with
nitric acid to expel the hydrochloric acid completely.    The residue is finally
treated with water faintly acidified with nitric acid and the solution filtered '
and the residue washed with water.    To the filtrate sufficient ammonia
is added to redissolve the antimony oxide at first separating, excess of
nitric acid being then added and the liquid filtered.    In the clear solution
the sulphuric acid, formed by oxidation of the sulphur in the sample, is
precipitated by means of barium nitrate.

* *

Commercial antimony generally contains small quantities of lead, copper,
iron, sulphur and, sometimes, bismuth, nickel and cobalt. Pure antimony
is silvery white, but the commercial metal has a slightly bluish tint owing to
the impurities present. It exhibits a marked tendency to crystallise and, indeed,
usually has a crystalline structure, which is manifested even on the outside by
large crystals resembling fern leaves, these being regarded—not always with
reason—as a sign of the purity of the metal.hen withoncen- the elec-